The present invention relates to a connecting assembly for fixing the tubular stem/stud of a portable lamp to the base of the same.
In the prior art, connection between a stem/stud and a base is made by using a screw thread and nut(s). Refer to FIG. 1(a) and (b). FIG. 1(a) shows a stem/stud (1) which has a threaded lower portion. The lower portion is screwed into a first nut (31') with a countersink in the top, and then inserted through a hole in a base (2), and is further fixed tight by a second nut (31"). FIG. 1(b) shows an improvement over the above structure, wherein the stem/stud (1) is necked to form a shoulder in order to eliminate the first nut. The threaded portion of the stem/stud (1) is inserted through holes made in a base (2) and a weight block (33). A nut (31) is threaded onto the stem/stud to fix all the parts together. Nevertheless, such structures are all related to threaded connection.
Following are some of the shortcomings of the prior art structures as mentioned above.
First, as is common knowledge, a threading procedure reduces the mechanical strength of a pipe. A remedy, pipe wall thickness has to be increased, which in turn will increase the cost. When a necking procedure is adopted, the pipe inside diameter is reduced. Besides, a necking procedure can not produce a right angle shoulder for butting which may prevent perpendicular assembly of the stem to the base.
Secondly, a screw nut is not only easy to loosen, but also has an axial dimension which is much larger than the wall thickness of a pipe. If a lock washer or such is used, the total axial height of the nut and the washer would be even larger. Moreover, use of a lock washer makes assembly more complicated. To prevent the nut from loosening, sometimes it is welded to the end of the threaded portion of the stem/stud. Even so, the connecting stem/stud can still turn in the base hole, if a proper locking device is not adopted.
Thirdly, after threading the end of the stem/stud, the stem/stud usually is painted or plated. Since usually fine thread is used, painting or plating he stems/studs can fill the threads so thay no longer mate with the nut. As known, a painting layer is much thicker than a plating layer. So during the painting procedure, even if only one drop of paint drops onto the threaded portion of the stem/stud, the result would be that the nut can no longer be threaded onto the stem/stud.
Fourthly, threading procedures are expensive; and the requirements for the raw material of the pipe which is to go through a threading procedure is also high, for the pipe diameter must be within a close tolerance, and the welding seam should be of the same strength as that of the pipe.
Fifthly, in the case of standard lamps, very often the user has to screw the tube stem to the base by himself, in which case the power supply cord located inside the stem/stud tube is often seriously wrung after assembly. One way to cope with this problem is to arrange the cord outside the stem/stud; another is to raise the base a bit higher by adding several legs to it, so that the power supply cord can run under the base into the tube. In both of the above cases, the cord is not running into the base at a fixed location. Besides, when the cord is made to run outside the stem tube, the lamp becomes bad-looking in appearance, and will easily be tipped over if someone stumbles over the cord. If, on the other hand, legs are added to raise the base to allow the cord to run beneath it, the cord which is usually in touch with the floor is apt to get worn when the lamp is moved here and there. Besides, raising the base to leave room for a cord to run means a higher center of gravity; and adding legs to the base will reduce the bottom area between base and floor (for instance, from a circle to an inscribed triangle if three legs are added). All these will result in that the lamp is much more easily tipped over.
Sixthly, a threaded connection is not suitable for use with pipes other than round ones. This largely limits the scope of raw materials.